Avoid unused braces lint for macro generated arguments by chenyukang · Pull Request #158791 · rust-lang/rust

chenyukang · 2026-07-05T04:41:26Z

This changes the unused_braces lint to avoid suggesting brace removal for macro arguments when those braces may affect macro_rules!.

But the fragment kind matters:

$e:expr matches an expression. Both 1 and { 1 } are expressions, so removing braces can still leave the macro matching the same kind of input.
$b:block only matches a block expression written with braces. { 1 } matches, but 1 does not.

So call_expr!({ 1 }) can usually be simplified to call_expr!(1), while call_block!({ 1 }) cannot.

It seems a more concrect report need a full macro_rules! matcher analysis, that seems too heavy for unused lint.

rustbot · 2026-07-05T04:41:31Z

r? @folkertdev

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folkertdev · 2026-07-05T17:04:08Z

                for arg in args_to_check {
+                    if callee_from_expansion && Self::block_wraps_expanded_expr(arg) {
+                        continue;
+                    }


this deserves a comment

View changes since the review

Maybe

Whether an expression is wrapped in a block can change what arm of a macro_rules! is taken. Don't report the braces as unused that might be the case.

folkertdev · 2026-07-05T17:04:49Z

        );
    }
+
+    fn block_wraps_expanded_expr(value: &ast::Expr) -> bool {


probably could use a comment too

View changes since the review

folkertdev · 2026-07-05T17:05:30Z

@@ -0,0 +1,38 @@
+//@ check-pass
+//@ run-rustfix
+


these days we often like to put a one-sentence description of what this is testing and why at the top of these files

View changes since the review

folkertdev · 2026-07-07T12:57:29Z

Lovely, thanks!

@bors r+ rollup

rust-bors · 2026-07-07T12:57:32Z

📌 Commit b50b5b2 has been approved by folkertdev

It is now in the queue for this repository.

…d-braces-macro, r=folkertdev Avoid unused braces lint for macro generated arguments Fixes rust-lang#158747 This changes the `unused_braces` lint to avoid suggesting brace removal for macro arguments when those braces may affect `macro_rules!`. But the fragment kind matters: - `$e:expr` matches an expression. Both `1` and `{ 1 }` are expressions, so removing braces can still leave the macro matching the same kind of input. - `$b:block` only matches a block expression written with braces. `{ 1 }` matches, but `1` does not. So `call_expr!({ 1 })` can usually be simplified to `call_expr!(1)`, while `call_block!({ 1 })` cannot. It seems a more concrect report need a full `macro_rules!` matcher analysis, that seems too heavy for `unused` lint.

…uwer Rollup of 11 pull requests Successful merges: - #158179 (std: unconditionally use `preadv`/`pwritev` on AArch64 macOS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158621 (disallow `extern "custom"` on wasm and spirv targets) - #158690 (delegation: support mapping of all arguments with `Self` type) - #158696 (Rename some `body_id` to `body_def_id`) - #158333 (Fix typetree generation for differentiated functions) - #158646 (powerpc64le_unknown_freebsd.rs: link with -lgcc) - #158791 (Avoid unused braces lint for macro generated arguments) - #158802 (Use `ci-mirrors` in `armhf-gnu` for {busybox, ubuntu rootfs} artifacts) - #158889 (tests: catch up with LLVM returning f128 on the stack) - #158905 (delegation: add constraints to new generic args)

…d-braces-macro, r=folkertdev Avoid unused braces lint for macro generated arguments Fixes rust-lang#158747 This changes the `unused_braces` lint to avoid suggesting brace removal for macro arguments when those braces may affect `macro_rules!`. But the fragment kind matters: - `$e:expr` matches an expression. Both `1` and `{ 1 }` are expressions, so removing braces can still leave the macro matching the same kind of input. - `$b:block` only matches a block expression written with braces. `{ 1 }` matches, but `1` does not. So `call_expr!({ 1 })` can usually be simplified to `call_expr!(1)`, while `call_block!({ 1 })` cannot. It seems a more concrect report need a full `macro_rules!` matcher analysis, that seems too heavy for `unused` lint.

…uwer Rollup of 18 pull requests Successful merges: - #157385 (Enable Enzyme on x86_64-apple) - #157561 (rustdoc: do not include extra stuff in span) - #158179 (std: unconditionally use `preadv`/`pwritev` on AArch64 macOS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158621 (disallow `extern "custom"` on wasm and spirv targets) - #158690 (delegation: support mapping of all arguments with `Self` type) - #158696 (Rename some `body_id` to `body_def_id`) - #158697 (Fixes for QNX SDP 8) - #158760 (Clarify that `LocalKey::try_with` may return `AccessError`) - #157801 (Rewrite safety requirements for `Allocator` impls) - #158333 (Fix typetree generation for differentiated functions) - #158646 (powerpc64le_unknown_freebsd.rs: link with -lgcc) - #158701 ( diagnostics: suggest type annotation for closure params on HRTB FnOnce mismatch) - #158791 (Avoid unused braces lint for macro generated arguments) - #158802 (Use `ci-mirrors` in `armhf-gnu` for {busybox, ubuntu rootfs} artifacts) - #158841 (Avoid final override ICE for RPITIT associated types) - #158889 (tests: catch up with LLVM returning f128 on the stack) - #158905 (delegation: add constraints to new generic args)

…uwer Rollup of 19 pull requests Successful merges: - #156016 (view-types: store view types in the AST) - #157385 (Enable Enzyme on x86_64-apple) - #158179 (std: unconditionally use `preadv`/`pwritev` on AArch64 macOS) - #158621 (disallow `extern "custom"` on wasm and spirv targets) - #158690 (delegation: support mapping of all arguments with `Self` type) - #158696 (Rename some `body_id` to `body_def_id`) - #158697 (Fixes for QNX SDP 8) - #158760 (Clarify that `LocalKey::try_with` may return `AccessError`) - #157801 (Rewrite safety requirements for `Allocator` impls) - #158085 (rustdoc: Fix sidebar heading order) - #158333 (Fix typetree generation for differentiated functions) - #158646 (powerpc64le_unknown_freebsd.rs: link with -lgcc) - #158701 ( diagnostics: suggest type annotation for closure params on HRTB FnOnce mismatch) - #158791 (Avoid unused braces lint for macro generated arguments) - #158802 (Use `ci-mirrors` in `armhf-gnu` for {busybox, ubuntu rootfs} artifacts) - #158841 (Avoid final override ICE for RPITIT associated types) - #158889 (tests: catch up with LLVM returning f128 on the stack) - #158905 (delegation: add constraints to new generic args) - #158922 (tests: clean up over-constraint on LLVM feature count) Failed merges: - #158617 (allow mGCA const arguments to fall back to anon consts)

Rollup merge of #158791 - chenyukang:yukang-fix-158747-unused-braces-macro, r=folkertdev Avoid unused braces lint for macro generated arguments Fixes #158747 This changes the `unused_braces` lint to avoid suggesting brace removal for macro arguments when those braces may affect `macro_rules!`. But the fragment kind matters: - `$e:expr` matches an expression. Both `1` and `{ 1 }` are expressions, so removing braces can still leave the macro matching the same kind of input. - `$b:block` only matches a block expression written with braces. `{ 1 }` matches, but `1` does not. So `call_expr!({ 1 })` can usually be simplified to `call_expr!(1)`, while `call_block!({ 1 })` cannot. It seems a more concrect report need a full `macro_rules!` matcher analysis, that seems too heavy for `unused` lint.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 5, 2026

rustbot assigned folkertdev Jul 5, 2026

folkertdev requested changes Jul 5, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 5, 2026

Avoid unused braces lint for macro-provided call arguments

b50b5b2

chenyukang force-pushed the yukang-fix-158747-unused-braces-macro branch from 27f37a2 to b50b5b2 Compare July 5, 2026 23:51

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 7, 2026

JonathanBrouwer mentioned this pull request Jul 7, 2026

Rollup of 9 pull requests #158909

Closed

JonathanBrouwer mentioned this pull request Jul 7, 2026

Rollup of 11 pull requests #158911

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JonathanBrouwer mentioned this pull request Jul 7, 2026

Rollup of 18 pull requests #158923

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JonathanBrouwer mentioned this pull request Jul 7, 2026

Rollup of 19 pull requests #158924

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rust-bors Bot merged commit 8e25cd2 into rust-lang:main Jul 8, 2026
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rustbot added this to the 1.99.0 milestone Jul 8, 2026

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Avoid unused braces lint for macro generated arguments#158791

Avoid unused braces lint for macro generated arguments#158791
rust-bors[bot] merged 1 commit into
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chenyukang:yukang-fix-158747-unused-braces-macro

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